This interface represents the remaining parts of an hyperplane after
other parts have been chopped off.

sub-hyperplanes are obtained when parts of an hyperplane are chopped off by other hyperplanes that
intersect it. The remaining part is a convex region. Such objects
appear in BSP trees as the intersection of a cut
hyperplane with the convex region which it splits, the chopping
hyperplanes are the cut hyperplanes closer to the tree root.